I need to give you an internet fistbump for this. I mean...you know what you can even do instead of The Holy Microservice? You can take parts of your API, facade them behind a different load balancer, and call into different instances of your monolith that only handle user management or billing or whatever. Un-run code's cost is, in the general case, basically zero--act like it. You don't need to do something like this, of course, unless your system has very spiky/expensive calls that have to be intelligently routed to systems that have capacity, but heck, you've just insulated yourself from load spikes and can granularly scale.

If you need to. You probably don't, and you definitely don't if you're struggling with 30 reqs/second. This isn't just YAGNI. This is YAHYBDI. You Are Hurting Yourself By Doing It. You need to write better code and examine the assumptions that have created the mess you're dealing with.